GoldenEye

GoldenEye is a trendsetter FPS from 1997. It swept the world with its gameplay, mechanics, and you'd be crazy not to mention the multiplayer. The modding has really grown from all the effort put into this game, from the entire community. There's guides, solo levels, mp levels, other types of hacks, action blocks to plug into maps, much documentation, and support can be found pretty easily. It has come a really long way!